Mi metas iom da pipro en la supon.

Metas is the present tense form of meti (to put).

• mi metas = I put / I am putting
• mi metis = I put / I was putting in the past
• mi metos = I will put

So this sentence is describing a present action.

Iom da means some amount of.

In this sentence:

• iom da pipro = some pepper

A useful way to think about it is:

• iom = some amount
• da = links that amount to a noun

So iom da pipro literally means something like an amount of pepper.

In Esperanto, words of quantity are often followed by da before the thing being measured or counted.

Examples:

• iom da akvo = some water
• multe da homoj = many people
• kilogramo da rizo = a kilogram of rice

So iom da pipro is the normal Esperanto pattern for some pepper.

A native English speaker may want to say iom pipro, but standard Esperanto uses iom da pipro.

Because pipro is part of the quantity phrase iom da pipro.

After da, the following noun normally stays in its basic form:

• iom da pipro
• multe da sukero
• glaso da akvo

The -n ending does not go on pipro here.

If the whole phrase needs -n, Esperanto usually puts it on the quantity word, not on the noun after da. For example:

• Mi volas iom da akvo.
• Mi trinkas iomon da akvo. — possible in grammar discussions, though in normal speech people often avoid making such phrases complicated

In your sentence, iom da pipro is just the thing being put, and it appears without an extra accusative marking on pipro.

This is a very common Esperanto point.

After a preposition like en (in), Esperanto normally does not use -n if it shows location:

• en la supo = in the soup (already there)

But if there is movement toward something, Esperanto often uses -n:

• en la supon = into the soup

So:

• Mi metas iom da pipro en la supon. = I put some pepper into the soup.
• Estas iom da pipro en la supo. = There is some pepper in the soup.

This -n is often called the accusative of direction.

The difference is:

• en la supo = location, no movement
• en la supon = direction, movement into

Compare:

• La kulero estas en la supo. = The spoon is in the soup.
• Mi metas la kuleron en la supon. = I put the spoon into the soup.

In your sentence, pepper is being moved from outside the soup to inside it, so supon is correct.

La is the definite article, meaning the.

So la supon means the soup. Esperanto uses la when the speaker and listener can identify which soup is meant.

For example, if you are talking about the soup currently on the table, la supo is natural.

If you said just en supon, that would sound more like into a soup, which is much less likely in an ordinary context.

Because pipro here is being used as an uncountable substance, like pepper in English.

In Esperanto:

• la pipro = the pepper
• pipro = pepper, pepper as a substance

Since iom da pipro already means some pepper, no article is needed.

This is similar to English, where we usually say some pepper, not some the pepper.

You might hear similar forms in some contexts, but iom da pipro is clearer and more natural if you want to emphasize some amount of pepper.

Why?

Because pipro is usually treated as a substance, and Esperanto often expresses an indefinite amount of a substance with a quantity phrase:

• iom da pipro
• iom da salo
• iom da akvo

So for a learner, Mi metas iom da pipro en la supon is the best model.

No, Esperanto word order is fairly flexible.

The neutral order here is:

• Mi metas iom da pipro en la supon.

But other orders are possible for emphasis, such as:

• En la supon mi metas iom da pipro.
• Iom da pipro mi metas en la supon.

Because Esperanto marks grammar with endings like -n, the sentence can often be rearranged more freely than in English.

Still, the original order is the most straightforward and natural for beginners.

Normally, yes, you should include mi.

Esperanto verbs do not change for person:

• mi metas
• vi metas
• li metas
• ŝi metas

Since metas alone does not tell you who the subject is, the pronoun is usually needed.

So Mi metas... is standard and clear.

Meti is a very common verb meaning to put or to place.

So:

• Mi metas pipron... = I put pepper...

It is a general verb for placing something somewhere.

Depending on context, Esperanto speakers might also use other verbs, such as aldoni (to add), but meti is perfectly understandable and very common for learners to know.

In Esperanto, the singular form is the basic form of the noun:

• pipro = pepper
• piproj = peppers

But with substances and mass nouns, the singular often works like English uncountable nouns:

• akvo = water
• sukero = sugar
• pipro = pepper

So iom da pipro does not mean one pepper. It means some pepper as a substance.

It breaks down like this:

• Mi = subject, I
• metas = verb, put / am putting
• iom da pipro = object-like quantity phrase, some pepper
• en la supon = prepositional phrase showing direction, into the soup

So the pattern is roughly:

subject + verb + thing + destination

That makes it a very useful model sentence for everyday Esperanto.